In recent years, the demand for portable electronic products such as notebook computers, video cameras and portable phones has increased sharply, and the electric vehicles, energy storage batteries, robots and satellites has been active developed. Accordingly, high-performance secondary batteries allowing repeated charging and discharging are being actively studied.
Secondary batteries commercially available at the present include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries and the like. Among them, the lithium secondary batteries have almost no memory effect compared to nickel-based secondary batteries and thus are in the limelight due to advantageous of free charging and discharging, low self-discharge rate and high energy density.
Battery packs are used in a wide variety of applications, and large capacities are often required for devices such as electric-driven vehicles or smart grid systems. In order to increase the capacity of the battery pack, the capacity of the secondary battery, namely the capacity of a battery cell itself, may be increased. However, in this case, the capacity increase effect is not large and there is a physical limitation on the size expansion of the secondary battery. Thus, generally, a battery pack in which a plurality of battery modules are connected in series and in parallel is widely used.
The battery pack often includes a battery management system (BMS) that manages battery modules. Further, the BMS monitors the temperature, voltage and current of the battery modules and controls the balancing operation, the cooling operation, the charging operation or the discharging operation of the battery pack based on the monitored state of the battery modules.
In order to monitor the current flowing through a charging/discharging path connected to the battery module, the BMS measures a voltage at both ends of a current sensor provided on the charging/discharging path and calculates the amount of current flowing through charging/discharging path by using the measured voltage at both ends. Here, if the current sensor is faulty and the current sensor comes to an open circuit state, the BMS calculates the amount of erroneous current and may determine that overcurrent flows in the charging/discharging path, based on the amount of erroneous current.
In order to diagnose whether the current sensor is in an open circuit state, a conventional technology for diagnosing whether the current sensor is in an open circuit state by using a current sensor diagnosis mode, which is a function of the BMS, has been proposed. However, during the current sensor diagnosis mode, the BMS is not able to measure the voltage, current and temperature of the secondary battery provided in the battery module.
In particular, the BMS should measure the voltage, current and temperature of the secondary battery and transmit the voltage, current and temperature to a micro controller unit (MCU) in the BMS or an electronic control unit (ECU) serving as a superior control device at a predetermined period, for example 1 ms intervals. However, if the current sensor diagnosis mode is performed, the voltage, current and temperature of the secondary battery is not able to be transmitted for a predetermined time, for example 100 ms.